FOREWORD

All the functions described in this page are used to add a rigidity mask to
LqrCarver
objects. Whenever one of these functions is called, a rigidity mask is activated for the whole image; the mask contains coefficients which modulate the value of the rigidity (which is set with
lqr_carver_init(3)) in different areas of the image.

It is very important to note that using no rigidity masks at all is equivalent to use a rigidity mask over the whole image with all the values set to
1.0, but, when first adding a rigidity mask to a
LqrCarver
object, all the pixels outside the affected area will have their rigidity set to zero; therefore, the functions
lqr_carver_rigmask_add_xy,
lqr_carver_rigmask_add_area
and
lqr_carver_rigmask_add_rgb_area
actually affect the whole image, despite their name.

All the functions must be called after
lqr_carver_init
and before
lqr_carver_resize. If called multiple times over the same area, new values will replace the old ones.

SETTING THE RIGIDITY MASK PIXEL BY PIXEL

The function
lqr_carver_rigmask_add_xy
sets the rigidity mask value of the
x,
y
pixel of the image loaded into the
LqrCarver
object pointed to by
carver

SETTING THE RIGIDITY MASK FROM A BUFFER

The function
lqr_carver_rigmask_add_area
adds a rigidity mask to an area of the image loaded in the
LqrCarver
object pointed to by
carver.

The parameter
buffer
must point to an array of
doubles
of size
width * height, ordered first by rows, then by columns.

The offset of the area relative to the image are specified through
x_off
and
y_off. The rigidity mask area can exceed the boundary of the image, and the offsets can be negative.

The values in the given
buffer
are scaled by the overall
rigidity
value set when calling the function
lqr_carver_init.

The function
lqr_carver_rigmask_add
can be used when the area to add is of the same size of the image loaded in the
LqrCarver
object and the offsets are
0.

SETTING THE RIGIDITY MASK FROM AN IMAGE

The functions
lqr_carver_rigmask_add_rgb_area
and
lqr_carver_rigmask_add_rgb
are very similar to
lqr_carver_rigmask_add_area
and
lqr_carver_rigmask_add, but use 8-bit multi-channel images as inputs.

The number of channels in the image is passed via the parameter
channels. The last channel is assumed to be the alpha (opacity) channel if
channels
is equal to
2
or greater than
3
(if this is not the case, use the previous functions).

The rigidity value is computed from the average of the colour channels, multiplied by the value of the alpha channel if present. For example, in RGBA images a white, nontransparent pixel is equivalent to a value of
1.0
when using a buffer in
lqr_carver_rigmask_add_area.